This invention relates to pouch machines and, more particularly, to an improved vertical sealer apparatus used in a continuous motion form, fill and seal machine having accelerated heating and cooling capabilities, respectively, for efficiently forming vertical seals along a folded web of heat-sealable material and for reducing undesirable vertical seal growth during intermittent operation of the vertical sealer apparatus.
The present application is related to the following United States patent applications filed on even date herewith and entitled: "Variable Count Direct Deposit Knife", by P. Dieterlen, Ser. No. 08/338,840 filed Nov. 14, 1994, pending; "Convertible Pitch Knife Apparatus", by P. Dieterlen, Ser. No. 08/338,848, filed Nov. 14, 1994, pending; "Convertible Pitch Pouch Machine", by F. Oliverio and B. Makutonin, Ser. No. 08/338,060, filed Nov. 14, 1994, pending, and "Tuck Roll With Improved Web Tension Control" by Martin Wildmoser and Frank G. Oliverio, Ser. No. 08/338,839, filed Nov. 14, 1994, pending, each of which is expressly incorporated herein by reference.
In pouch machines of the known art, such as disclosed in U.S. Pat. No. 3,597,898 which is herewith incorporated herein by reference, a flat web of heat sealable material is continuously fed from upstream of the pouch machine to be longitudinally folded upon itself by a plow or similar device. In this form, the thus-folded web is fed about a sealer which contacts the folded web along vertical heated land areas to form transverse vertical seals and, thus, a series of open pouches along the web. In this way, the web of open pouches is passed around a filler wheel, filled with product and then sealed along the top edge of the web. The web of filled pouches then passes downstream to a motor-driven rotary knife apparatus which cuts the web along the transverse vertical seals into separate individual pouches for subsequent cartoning or other secondary packaging.
In a typical apparatus for making vertical seals along a folded web, the apparatus includes a metallic rotary drum having a predetermined number of radially extending, outwardly facing sealing surfaces. The outwardly facing sealing surfaces of the drum lie in a circle and are circumferentially spaced such that the sealing surfaces contact the web along defined transverse areas of the web as it is passed around the rotary drum. The drums of the known art are typically cast of steel or similar material wherein the radially extending sealing surfaces are interconnected by metallic web areas which lie inwardly from and between the sealing surfaces.
In known operation of the vertical sealer, the sealing surfaces are heated by individual heaters at each sealing surface to a predetermined temperature such that the folded web, typically made of a single ply heat-sealable film or laminate of heat sealable film to paper or metallic foil, for example, reacts to the heated sealing surfaces to form transverse seals across the moving web, and thus, a train of pouches having open mouths is formed for receiving product downstream at the filler wheel. The web is typically preprinted with labels in such a fashion that the labels are spaced corresponding to the pitch of the sealing surfaces. When the web is properly registered with the vertical sealer in accordance with U.S. Pat. No. 4,316,566, for example, which is herewith incorporated herein by reference, each label is centered between a pair of transverse seals formed by the vertical sealer whereby the rotary knife apparatus cuts the web along a centerline of each transverse vertical seal to separate the web into symmetrical individual pouches.
In operation of continuous motion form, fill and seal machines, it is common for the vertical sealer apparatus and web to be stopped while adjustments are made to various aspects of the machine or to up- or downstream equipment. When this occurs, the web is held stationary against the heated sealing surfaces and the vertical seals have a tendency to grow in width as a result of the continuous heat being applied to the web. Furthermore, the web may even change color or burn as a result of the continuously applied heat. Even if the heat source is turned off, residual heat in the sealing surfaces can be deleterious to the web.
These undesirable conditions can be exacerbated when the web includes an inner metallic foil which conducts the heat from the sealing surfaces through the web, thereby accelerating the web's vertical seal growth and discoloration. As the web is then moved in later operation, the web either typically breaks as a result of being weakened by the continuous heat or the pouches formed by the vertical seals are now too small between the enlarged seals to receive the desired quantity of product fill. In either case, a portion of the web must now be discarded as scrap before proper operation of the pouch form, fill and seal machine can be continued.
To cure the problem of continuously heating the web during a shutdown, it was known before the present invention was made to include a ring of air outlets below the vertical sealer drum and concentric with the web being passed around the drum. In this way, compressed air is directed at the web through the air outlets in an attempt to cool the web during the shutdown while the heaters remain operational.
However, while this advance has been useful, the compressed air system in such a design adds cost and complexity to the pouch form, fill and seal machine. Moreover, the direction of the compressed air typically cannot be concentrated at critical web areas along either side of the heated sealing surfaces to further cool the web and prevent undesirable seal growth at these critical areas. Moreover, the continuously operational heaters reduces the cooling effect provided by the compressed air.
Furthermore, in rotary drums of the known art, the material and design of the drums typically does not provide for acceleration of the heating and cooling processes. For example, as the individual sealing surfaces are heated in the known drums, some of that heat is also transferred to the interconnecting web areas between the sealing surfaces. Thus, more energy and time is required to heat the sealing surfaces to a predetermined temperature as a result of the heat being lost to the web areas. After the sealing surfaces are heated to the predetermined temperature and a shutdown occurs, the vertical sealer drum becomes a large heat sink due to the heated web areas and the high thermal retention property of the steel drum. Residual heat from the drum and heat supplied from the operational heaters is continued to be applied to the web along the sealing surfaces during the shutdown, thereby resulting in undesirable vertical seal growth, discoloration and reduction of web strength.
Accordingly, an objective of the present invention has been to provide a vertical sealer apparatus used in a continuous motion form, fill and seal machine which will reduce undesirable vertical seal growth along a folded web of heat-sealable material during intermittent operation of the apparatus.
Another objective of the present invention has been to provide a vertical sealer apparatus which provides for accelerated heating of the sealing surfaces of the apparatus with minimal heat loss through the drum.
It has been a further objective of the present invention to provide a vertical sealer apparatus which has low thermal inertia properties for providing accelerated cooling of the sealing surfaces during intermittent operation of the apparatus.